From 83a0e939a40026ddb4131959c507ef7a49df9c7b Mon Sep 17 00:00:00 2001
From: gammazero <gammazero@users.noreply.github.com>
Date: Mon, 3 Apr 2023 08:18:57 -0700
Subject: [PATCH] Add unit test for unexpected eof

---
 cid.go      |  3 +++
 cid_test.go | 10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/cid.go b/cid.go
index 6e36764..f182424 100644
--- a/cid.go
+++ b/cid.go
@@ -717,6 +717,9 @@ func (r *bufByteReader) ReadByte() (byte, error) {
 // It's recommended to supply a reader that buffers and implements io.ByteReader,
 // as CidFromReader has to do many single-byte reads to decode varints.
 // If the argument only implements io.Reader, single-byte Read calls are used instead.
+//
+// If the Reader is found to yield zero bytes, an io.EOF error is returned directly, in all
+// other error cases, an ErrInvalidCid, wrapping the original error, is returned.
 func CidFromReader(r io.Reader) (int, Cid, error) {
 	// 64 bytes is enough for any CIDv0,
 	// and it's enough for most CIDv1s in practice.
diff --git a/cid_test.go b/cid_test.go
index f0c6ad5..36fba76 100644
--- a/cid_test.go
+++ b/cid_test.go
@@ -795,6 +795,16 @@ func TestFromReaderNoData(t *testing.T) {
 	if n != 0 {
 		t.Fatal("Expected 0 data")
 	}
+
+	// Read byte indicatiing more data to and check error is ErrInvalidCid.
+	_, _, err = CidFromReader(bytes.NewReader([]byte{0x80}))
+	if !errors.Is(err, ErrInvalidCid{}) {
+		t.Fatal("Expected ErrInvalidCid error")
+	}
+	// Check for expected wrapped error.
+	if !errors.Is(err, io.ErrUnexpectedEOF) {
+		t.Fatal("Expected error", io.ErrUnexpectedEOF)
+	}
 }
 
 func TestBadParse(t *testing.T) {